Alcohol use, particularly among those in the criminal justice system, imposes tremendous costs on individuals and society. Policymakers are searching for ways to mitigate the threat alcohol poses to public health and safety even as budgetary pressures force them to consider keeping low-level offenders with alcohol problems in the community rather than incarcerated. With more than 5 million individuals under community supervision, even small reductions in alcohol consumption among this population can improve public health and public safety. This study proposes a rigorous evaluation of a large-scale and innovative program in South Dakota that has received significant attention as a successful approach to reducing alcohol consumption in community corrections settings. South Dakota's 24/7 Sobriety Program (24/7) requires that offenders submit to breathalyzer tests twice per day. Those testing positive or missing a test face an immediate, but brief, jail term. Since 2005 there have been more than 13,000 participants and our calculations suggest participation rates of at least 5% among all males aged 22-40. While 24/7 is touted as a national model and is being considered and adopted in other states, there is no peer-reviewed scientific evidence of its effectiveness or cost-effectiveness. Our proposed evaluation of 24/7 is innovative in its methods, access to data, and scope. The quasi- experimental approach, which exploits the staggered implementation of 24/7 across counties and offender types, is necessary to evaluate the large-scale implementation in the absence of random assignment. The evaluation is also strengthened by exceptional access to data on participants and non-participants and by the broader incident-level data on alcohol-related harms in the community. The specific aims are: Aim 1: Document the implementation and utilization of 24/7 across counties and offender types. Aim 2: Identify predictors of 24/7 program violations among participants. Aim 3: Estimate the effect of 24/7 participation on individual-level recidivism outcomes. Aim 4: Estimate the effect of 24/7 on health and social outcomes including alcohol-related traffic accidents, hospital admissions, arrests, and reported crimes. Aim 5: Monetize the costs and benefits of 24/7. The goal of this study is to provide policymakers and stakeholders within and beyond South Dakota with rigorous evidence regarding 24/7's effectiveness and cost-effectiveness to inform the ongoing policy debate about how to effectively use alcohol testing to reduce alcohol misuse and its consequences. This information is critical as fiscally-constrained states seek to reduce incarceration and effectively manage those with alcohol problems in the community while safeguarding public health and safety.